Variable-Capacity Cooling

Data center systems are designed to handle peak loads, which rarely exist. Consequently, operating efficiency at full load is rarely a good indication of actual operating efficiency. Newer technologies, such as Digital Scroll compressors and variable frequency drives in computer room air conditioners (CRACs), allow high efficiencies to be maintained at partial loads. Digital Scroll compressors allow the capacity of room air conditioners to be matched exactly to room conditions without turning compressors on and off. Typically, CRAC fans run at a constant speed and deliver a constant volume of air flow. Converting these fans to variable frequency drive fans allows fan speed and power draw to be reduced as load decreases. A 20 percent reduction in fan speed provides an almost 50 percent reduction in fan power consumption. These drives are available in retrofit kits that make it easy to upgrade existing CRACs with a payback realized in less than one year.